ios - 作为构造函数关闭？

Question

我在 objc io 书中看到过这样的示例

callback(Result {
    if let e = error {
       throw e
    }

    guard let d = data else {
       throw NoDataError()
    }

    return try JSONDecoder().decode(User.self, from: d)
})

回调在哪里

“callback: @escaping (Result<User, Error>) -> ()

似乎 Result(Swift 定义的枚举类型)正在使用闭包来创建自身？

但我没有看到任何相关文档

Answer 1

有文档。

该表达式表示 init(catching:) 的尾随闭包语法方法Result 。说明是

Creates a new result by evaluating a throwing closure, capturing the returned value as a success, or any thrown error as a failure.

完整的语法是

callback(Result(catching: {
    if let e = error { 
       throw e 
    }

    guard let d = data else { 
       throw NoDataError() 
    }

    return try JSONDecoder().decode(User.self, from: d)
    })
)

另请参阅Preserving the Results of a Throwing Expression